An apparatus for detecting touch (hereinafter, a touch detecting apparatus) includes a touch panel and recognizes a user's screen touch or gesture as input information. The touch panel provided in the touch detecting apparatus may be categorized into an analog resistive type, a capacitive overlay type, a surface acoustic wave type and an infrared type based on a method for touching. The capacitive overlay type apparatus for detecting touch receives attention of a wide public, because a user can implement multi touch input thereto.
Such a capacitive overlay touch panel uses a principle that capacity is varied by touch input applied to a transparent conductive film or glass. As capacitances are generated, more electric charge accumulates in coordinates input by touch than coordinates not input by touch. A detection circuit analyzes a difference of the electric charges between the coordinates and detects the touch input coordinates based on the analyzed difference.
As the signal detected by the detection circuit reflects presence of touch input more accurately, the accuracy for presence of touch is increased more. However, the size of the detection signal is not determined only by variation of the capacitances generated by touch input. For instance, the detection signal could be mixed with the noise of a capacitance generated by a correlation with a display device arranged behind a touch panel, the noise of a capacitance generated by wiring nearby and the other external noises. Such the noise signals might deteriorate accurate determination of presence of touch input and determination of the number and coordinates of touch inputs in a touch detecting apparatus, especially, in a multi touch detecting apparatus. In case a touch panel is getting enlarged, a physical curling of a touch panel could be increasingly performed and the problem of the noise of a capacitance generated by the correlation with the display arranged behind the touch panel is getting severe.